# Composite data types 
# Only objects that can be hashed can be used as dict key.
# fixed datatype, such as [float frozenset int str tuple] all can be used as dict key
# Variable datatype, such as [dict set list] cannot be used as dict key

import os 
file_sizes = {name: os.path.getsize(name) for name in os.listdir('.')
                if os.path.isfile(name)}
print(file_sizes)